1. Field of the Invention
The present invention relates to an information storage medium equipped with a memory device such as a flash memory, EEPROM or magnetic disk memory used as an external storage medium in an information processor, and also relates to a security method thereof.
2. Description of the Prior Art
Regarding an external storage medium for use in a battery-powered portable information terminals, there are many types of information storage media including various IC cards, particularly a category termed flash ATA-PC card (hereinafter referred to simply as PC card). FIG. 7 is a functional block diagram of an information storage medium representing a conventional flash ATA-PC card. In this diagram, there are shown an information storage medium 1e; a host apparatus 2; a central controller 3e; a memory device 4 such as a flash memory, EEPROM or magnetic disk memory; a host interface circuit 5; a central processing unit (CPU) such as a microprocessor (MPU); a sector buffer 7; a bus control circuit 8; an ECC (error correction code) circuit 11; and a memory control circuit 12.
The central controller 3e consists of the host interface circuit 5, the CPU 6, the sector buffer 7, the bus control circuit 8, the ECC circuit 11 and the memory control circuit 12, all of which can be mounted on a sing IC (integrated circuit) chip. The ECC circuit 11 has a function of correcting, as well as detecting, up to a certain number of bit errors.
Next, the operation will be described.
First in a mode to write data in such information storage medium 1e, the host apparatus 2 writes new file data in a data area of the information storage medium 1e after writing, at predetermined logical addresses by an OS which handles media with a disk type architecture, directory entry information composed of file name, size, generation date and so forth, and also FAT (file allocation tab) information indicative of a logical storage location for the file data. At this time, the data stored temporarily in the sector buffer 7 via the host interface circuit 5 is written, in the form of un-encrypted data (i.e., in a form which is not encrypted to enhance security), by the central controller 3e in a predetermined area (header area, sector data area or ECC area) in accordance with the logical address value specified by the host apparatus 2.
And in a read mode, the CPU 6 sequentially reads out the stored data from the memory device 4 via the sector buffer 7 while communicating with the host apparatus 2 via the host interface circuit 5. Since the stored data is in the form of un-encrypted data in this case, no manipulation is executed for data conversion.